Methods of preparing 6-substituted-11-aminoalkylidenemorphanthridines are described in Belgian Pat. No. 732,405, British Patent No. 1,207,116, and U.S. Pat. No. 3,692,906. Among the methods described are processes for dehydrogenating the corresponding 5,6-dihydromorphanthridine with oxidizing agents such as chromic acid, peroxide, permanganate or manganese dioxide.